Portable medical devices are useful for patients that have conditions that must be monitored on a continuous or frequent basis. For example, diabetics are usually required to modify and monitor their daily lifestyle to keep their blood glucose (BG) in balance. Individuals with Type 1 diabetes and some individuals with Type 2 diabetes use insulin to control their BG levels. To do so, diabetics routinely keep strict schedules, including ingesting timely nutritious meals, partaking in exercise, monitoring BG levels daily, and adjusting and administering insulin dosages accordingly.
The prior art includes a number of fluid infusion devices and insulin pump systems that are designed to deliver accurate and measured doses of insulin via infusion sets (an infusion set delivers the insulin through a small diameter tube that terminates at, e.g., a cannula inserted under the patient's skin). In lieu of a syringe, the patient can simply activate the insulin pump to administer an insulin bolus as needed, for example, in response to the patient's high BG level.
A typical infusion pump includes a housing, which encloses a pump drive system, a fluid containment assembly, an electronics system, and a power supply. The pump drive system typically includes a small drive motor or motor assembly (DC, stepper, solenoid, or other varieties) and drive train components such as gears, screws, and levers that convert rotational motor motion to a translational displacement of a stopper or piston of a fluid reservoir. The fluid containment assembly typically includes the fluid reservoir with the actuation piston, tubing, and a catheter or infusion set to create a fluid path for carrying medication from the reservoir to the body of a user. The electronics system regulates power from the power supply to the motor. The electronics system may include programmable controls to operate the motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period.
Some fluid infusion devices use sensors and alarm features designed to detect and indicate certain operating conditions, such as non-delivery of the medication to the patient due to a fluid path occlusion. In this regard, a force sensor can be used in a fluid infusion device to detect the amount of force imparted by the motor assembly and/or an actuator to the piston of the fluid reservoir. The force sensor in such a fluid infusion device could be positioned at the end of the drive motor assembly that actuates a rotatable drive screw, which moves an actuator, which in turn advances the piston of the reservoir. With such an arrangement, the force applied to the force sensor by the drive motor assembly is proportional to the pressure applied to the piston as a result of power supplied to the drive system to advance the piston. Thus, when a certain force threshold (a set point corresponding to an occlusion condition) is reached, the fluid infusion device is triggered to generate an alarm to warn the user.
Some fluid infusion devices use replaceable fluid reservoirs that are secured in the reservoir cavity of the device and actuated by the drive assembly. One form of infusion pump utilizes a removable threaded cap that accommodates replacement and refilling of fluid reservoirs, and that is used to seat and secure the fluid reservoir in the housing of the pump. Assuming that the pump had previously completed a rewind operation, the user unscrews the threaded cap to remove an empty reservoir, refills the reservoir or replaces the old reservoir with a new reservoir, and reinstalls the threaded cap to secure the filled reservoir in place. After installing a reservoir, the pump is operated to perform a seating action during which the actuator is advanced forward until it reaches and seats with the piston of the fluid reservoir. The force sensor may be used during the seating action to detect when proper seating has occurred.
The reservoir cavity is typically sealed to inhibit ingress of fluid and contaminants, such that the fluid reservoir and electronics inside the housing remain protected. Although sealed to inhibit fluid and particulates, the reservoir cavity may include a vent structure or element that allows air to flow into and out of the reservoir cavity. The reservoir cavity vent is desirable to equalize the pressure inside the reservoir cavity, regardless of the position of the reservoir actuator. If this vent is blocked, however, pressure could increase inside the reservoir cavity during seating operations because the forward advance of the actuator reduces the interior volume of the reservoir cavity, which in turn results in increased pressure (due to the unvented and sealed state of the reservoir cavity). Unpredictable buildup of pressure in this manner is undesirable because it can impact the accuracy of the reservoir seating operation, which relies on force measurements as mentioned above.
Accordingly, it is desirable to have an improved reservoir seating technique for fluid infusion devices. In addition, it is desirable to have a methodology for detecting a blocked reservoir cavity vent during a reservoir seating operation. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.